> I added a new "loadbalance" feature to OMPI today in r18252.
>
> Brief summary: adding --loadbalance to the mpirun cmd line will
> cause the
> round-robin mapper to balance your specified #procs across the
> available
> nodes.
>
> More detail:
> Several users had noted that mapping byslot always caused us to
> preferentially load the first nodes in an allocation, potentially
> leaving
> other nodes unused. If they mapped bynode, of course, this wouldn't
> happen -
> but then they were forced to a specific rank-to-node relationship.
>
> What they wanted was to have the ranks numbered byslot, but to have
> the ppn
> balanced across the entire allocation.
>
> This is now supported via the --loadbalance cmd line option. Here is
> an
> example of its affect (again, remember that loadbalance only impacts
> mapping
> byslot):
>
> no-lb lb bynode
> node0: 0,1,2,3 0,1,2 0,3,6
> node1: 4,5,6 3,4 1,4
> node2: 5,6 2,5
>
>
> As you can see, the affect of --loadbalance is to balance the ppn
> across all
> the available nodes while retaining byslot rank associations. In
> this case,
> instead of leaving one node unused, we take advantage of all available
> resources.
>
> Hope this proves helpful
> Ralph
>
>
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